staging: board: Set PM domain before probe

PM domains shouldn't be modified after a device is probed, so set it
before device registration to be sure of that.

In the future the PM domain pointer will be set through a setter that
will WARN if the device has been probed already.

Signed-off-by: Tomeu Vizoso <tomeu.vizoso@collabora.com>
Tested-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>